Diphosphametacyclophanes: Structural and Electronic Influences of Substituent Variation within a Family of...

The condensation of MeP(SiMe₃)₂ with a series of 5-substituted isophthaloyl chlorides (5-R'C₆H₃-2,6-{C(O)Cl}₂) affords the diphosphametacyclophanes m-{-C(O)-C₆H₃-5-R'-(C(O)PMe)}₂ (R' = I, Me, Bu, Ph, and p-NCC₆H₄); the analogues m-{-C(O)-C₅H₃N-(C(O)PMe)}₂ and m-{-C(O)-C₆H₄-(C(O)PPh)}₂ are similarly obtained in preference to higher oligomers, in contrast to precedent reports. The cyclophanes all adopt butterfly-like conformations in the solid state with the P-organyl substituents adopting mutually exo arrangements. Structural and computational data suggest the nature of the 5-R substituent is key in directing the inter-ring angle and the extent of LUMO stabilization about the diketophophanyl scaffold. The latter is substantiated by UV/vis spectroscopy and cyclic voltammetry, which demonstrate these cyclophanes to be appreciably comparable to the diketophosphanyl systems commonly explored in the context of organic electronic materials; intriguingly, the distinct dikeophosphanyl moieties within the macrocycles appear effectively "insulated" by the macrocycle geometry, rather than acting as a through-conjugate.